Helico-Axial Submersible Pump

ABSTRACT

An electrical submersible pump (ESP) having a helico-axial centrifugal pump to lift fluid from a wellbore, and a submersible permanent magnet motor (PMM) to drive the helico-axial centrifugal pump.

TECHNICAL FIELD

The present techniques relate to submersible pumps, such as for oil and gas wells.

BACKGROUND

A submersible pump may have a submersible or hermetically-sealed motor close-coupled to the pump body. The assembly may be submerged in the fluid to be pumped and thus generally avoid pump cavitation. Submersible pumps typically push the pumped fluid to the surface. A submersible pump system may have both downhole components and surface components. The downhole components may include a motor, seal, intake, pump, motor lead extension (MLE) and cable. Additional downhole components may include data acquisition instrumentation, cable bands and cable protectors, gas separator, by-pass system, auto flow valves, and check and drain valves. The surface components may include a step down transformer, electrical junction box, and motor controller such as a fixed speed controller or variable speed controller with step up transformer.

Applications of submersible pumps include drainage, sewage pumping, sewage treatment plants, general industrial pumping, slurry pumping, pond filters, seawater handling, fire-fighting, water well and deep well drilling, offshore drilling rigs, artificial lifts, mine dewatering, and irrigation systems. Submersible pumps may be lowered down a borehole and used for residential, commercial, municipal and industrial water extraction, and in water wells, oil and gas wells, and so forth.

Submersible pumps in oil production may provide for “artificial lift.” These pumps are typically electrically powered and commonly referred to as an electrical submersible pump (ESP). ESPs can be centrifugal pumps operated in a vertical position.

SUMMARY

An aspect relates to an electrical submersible pump (ESP) system having a pump including a helico-axial centrifugal pump to lift fluid from a wellbore, and a motor including a submersible permanent magnet motor (PMM) to drive the helico-axial centrifugal pump. Another aspect relates to an ESP having a multi-stage helico-axial centrifugal pump for insertion into a wellbore to pump fluid from the wellbore, and a submersible PMM for insertion into the wellbore and to drive the multi-stage helico-axial centrifugal pump. Yet another aspect relates to a method of operating an ESP including pumping, by the ESP, fluid from a wellbore, wherein the ESP has a multi-stage helico-axial centrifugal pump and a PMM.

The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram of an electrical submersible pump (ESP).

FIG. 2 is a diagram of the FIG. 1 ESP installed in a wellbore.

FIG. 3 is a diagram of an ESP having a radial or mixed-flow pump and an induction motor.

FIG. 4 is a diagram of an ESP having a multi-stage helico-axial pump and a permanent magnet motor.

FIG. 4A is a perspective view of internals of a pump stage of the helico-axial pump of FIG. 4.

FIG. 5 is a block flow diagram of a method of operating an ESP.

DETAILED DESCRIPTION

Multistage “helico-axial” pumps may pump mixtures of oil, natural gas, water, and sand with gas volume fractions from zero to at least 97%. Some electrical submersible pumps (ESP) for ESP applications on oil and gas wells may be a “partial helico-axial” pump with a helico-axial portion or helical-axial gas handler disposed below a typical pump such as a radial or mixed-flow pump. In other words, the ESP may incorporate a small helico-axial pump with few stages installed below the conventional pump to handle higher gas volume fractions. However, the technique of a helico-axial portion in combination with a typical pump can have limitations due to the moderate rotation speed provided by the induction motor and due to the utilization of the radial or mixed-flow typical pump.

Helico-axial stages may benefit from a high specific speed (Ns) relying on high rotation speed including even higher rotation speeds for applications where the impeller diameter is relatively small due to space limitation such as in the case of oil and gas wells. These multi-phase pump stages typically perform better at higher rotation speed for higher gas volume fractions. Embodiments herein employ a permanent magnet motor (PMM) for the ESP for oil or gas wells and which can operate at higher speeds such as 7000 revolutions per minute (rpm) or above. Moreover, a product line of helico-axial pumps having a range of capacities and diameters provide higher lift without the radial or mixed flow pumps to deliver the desired flow rates. Gas volume fractions up to 97% or greater can be handled. The pumps operate at up to 7000 rpm or greater via the PMM to handle high free gas in oil wells and may compose the product line of centrifugal pumps with the helico-axial stages or similar type stages. These innovative pumps include a range of flow-rate capacity pumps such as for ESP series sizes (for example, 338, 400, 513, 538, and 562). Unlike typical ESPs, the pump intake and motor protector may be configured for the higher rotation speed. In contrast, the ESP with a radial pump or screw-stator pump employs the typical intake and protector. Indeed, the ESPs with a radial pump, mixed-flow pump, or screw-stator pump, and the associated ESP subcomponents, are not configured or sized to handle the high rotation speeds of the present techniques.

The term “axial” may mean forming or relating to an axis, or around an axis, or in direction along an axis. A category of centrifugal pumps is an axial-flow pump. The axial-flow pump may have a propeller-type of impeller running in a casing, housing or diffuser and driven by a motor. In operation of the axial-flow pump, pressure is developed by the flow of fluid over the blades of the impeller, and the fluid may be pushed in a direction generally parallel to the pump shaft of the impeller. The fluid may enter the impeller axially, and fluid discharge axially or nearly axially. Further, the prefix “helico” generally means spiral, spiral-shaped, or helical. A helico-axial pump is a type of pump. FIG. 4A is a pump stage of an exemplary helico-axial pump. As discussed below, a stage of a helico-axial pump may have a rotating part (impeller) and a stationary part (diffuser).

Techniques employing radial or mixed-flow stages pumps, or moderate pump-rotation speeds of 2000 revolutions per minute (rpm) to 4000 rpm, are generally inadequate to handle high gas-volume fraction such as in oil and gas wells. Indeed, such pumps may become locked by gas in oil-well applications. Thus, certain embodiments herein employ a helico-axial pump at a higher speed and with no radial or mixed-flow pump. The helico-axial pumps may have open-type stages which are generally not significantly susceptible to becoming gas locked. In order to increase pressure to the pumped fluid, some embodiments of these helico-axial pumps have several stages and operate, via a PMM, at rotational speed in a range of 4000 rpm to 7000 rpm or greater. An induction motor may be avoided and instead the electrical submersible PMM employed for these pumps for oil wells and which can be operated up to 7000 rpm or above.

Embodiments of the present techniques are directed to high-speed multi-stage helico-axial pumps to be used as ESPs to lift hydrocarbons, in particular, multi-phase hydrocarbons, in a hydrocarbon reservoir to a surface through a wellbore. A helico-axial pump may include several stages in which each stage typically has an impeller and diffuser with a helico-axial profile positioned within a housing. Multiple helico-axial pumps can be coupled in tandem to achieve the desire lifting pressure without coupling conventional pumps having radial or mixed-flow stages. The helico-axial pumps can be coupled to a sub-assembly which may include an intake, gas separator, motor protector, and permanent magnet motor. The PMM can rotate at high speeds (for example, about 7000 rpm or higher), which is higher than the speed at which radial or mixed-flow ESPs with an induction motor rotates (for example, between 2000 and 4000 rpm). With the multi-stage helico-axial pump, the high rotational speeds enhances the capacity to handle multiphase fluids with gas volume fractions as high as 97% through the helico-axial pump. This fraction is higher than the gas volume fraction the radial or mixed-flow ESPs can handle (for example, up to 70%).

In general, the electrical submersible pump, typically called an ESP, may give artificial-lift for lifting moderate to high volumes of fluids from oil and gas wellbores. These volumes may range from a low of 150 barrels/day (B/D) to as much as 25,000 B/D or more. Variable-speed controllers can in some arrangements extend the range. ESP systems can pump a variety of production fluids toward the surface, such as crude oil and brine. The pumped fluids may include oil, gas, natural gas, liquid petroleum products, disposal/injection fluids, solids or contaminates, carbon dioxide (CO2) and hydrogen sulfide (H2S) gases, treatment chemicals, and so forth. Indeed, some ESPs can handle corrosive fluids and abrasive contaminants such as sand.

ESP systems may employ a centrifugal pump below the level of the reservoir fluids. Moreover, submersible pumps may be single-stage pumps or multi-stage pumps. For instance, ESPs can be multistage centrifugal pumps operated in a vertical position, deviated position, or horizontal position. The pump is typically connected to an electric motor which may be a relatively-long electric motor in some examples. Indeed, an ESP is typically relatively long and slim, and may be disposed in wellbores to lift or pump fluids from the wellbores. Some ESPs coupled to production tubing can fit and operate in wellbore casings as small as 4.5 inch outside-diameter or smaller. The ESP components, such as the pump, seal, and motor, may be manufactured in varying lengths and connected in series. The arrangement and configuration may vary depending on the application. The motor protector or seal section may protect the motor from contamination by well fluid, absorb thrust from the pump, and equalize pressure between the wellbore and motor. As for deployment, the downhole portion of the ESP system may be installed via the bottom of the tubing string. Moreover, an electric cable generally runs the length of the well, connecting the pump to a surface source of electricity, a transformer, and surface control equipment.

As discussed, one embodiment of the present techniques is an ESP or ESP system that is a multi-stage high-speed helico-axial centrifugal ESP. In operation, the ESP pumps or lifts hydrocarbon from a wellbore. In this example, the ESP has a submersible permanent magnet motor (PMM) and does not incorporate an induction motor. Moreover, this ESP does not incorporate a radial pump, mixed-flow pump, hybrid pump, or screw-stator pump. Again, the pump is a high-speed helico-axial pump type. The ESP or ESP pump may have a rotation speed in the range of 4000 rpm to 7000 rpm (or greater) to give a relatively-high specific speed (Ns). The ESP may pump hydrocarbon having a gas volume fraction up to 97% or more. See FIG. 4 as an example.

Turning now to the drawings, FIG. 1 is an ESP system having an ESP 100 and ESP surface components 110. In operation, the ESP 100 pumps or lifts fluid from a well or wellbore. The fluid may be or include hydrocarbon such as oil and gas. The ESP 100 has a pump portion or pump 102, and a motor portion or motor 104 that drives the pump 102. The pump 102 and motor 104 are sized and arranged for insertion downhole into a wellbore. Depending on the application, the pump 102 and motor 104 may be sized to fit into a wellbore casing having an outer diameter as small as 4.5 inches or smaller. Furthermore, the pump 102 may be sized to lift the volume of fluid production from the wellbore. In certain examples, the motor 104 may be powered from the surface via, for example, a submersible electric cable.

In some examples, the pump 102 is a multi-stage centrifugal pump. The pump 102 typically has an inlet 106 as an intake or fluid suction on a lower part of the pump 102 or below the pump 102. In operation, the pump 102 receives fluid through the inlet 106 and discharges the pumped fluid from an opposite end on an upper part of the pump 102, as indicated by arrow 108. The pump 102 shaft, driven by the motor 104, rotates the pump 102 impellers or vanes in operation and can be connected to an intake or gas separator and the protector by a mechanical coupling at a bottom portion of the pump 102. Fluids enter the pump 102 through the inlet 106 which may have an intake screen in some embodiments. The fluids are lifted by the pump 102 stage or stages. The fluid may enter the impeller near the shaft and exit the impeller near or on an outer diameter (OD). A diffuser may redirect fluid into the next impeller. By stacking impellers and diffusers (multi-staging), the desired lift or total dynamic head (TDH) may be achieved. Other ESP parts may include radial bearings or bushings distributed along the length of the pump 102 shaft providing radial support to the pump 102 shaft.

The pump 102 may be a radial-flow pump, a mixed-flow pump, a screw-stator pump, and the like. However, as indicated below with respect to FIG. 4, the pump 102 may instead be a multi-stage helico-axial centrifugal pump. In certain examples, the motor 104 is an induction motor. Yet, as indicated below with respect to FIG. 4, the motor 104 may instead be a submersible PMM. In all, the pump 102 may be a multistage centrifugal pump, a helico-axial centrifugal pump, a radial pump, a mixed-flow pump, a screw-stator pump, or any combinations thereof, and the like. The motor 104 may be an induction motor, a three-phase induction motor, a PMM, and so on.

ESP systems 100 include components in addition to the pump 102 and motor 104. For instance, the ESP system 100 generally includes a pump fluid intake or inlet 106 on a lower portion of the pump 102 or under the pump 102. The ESP 100 may include a seal section or motor seal disposed between the pump 102 and motor 104. The seal section may be a protector, equalizer, balance chamber, and the like. If a protector is employed, the protector may be a labyrinth protector, bag protector, and so on. The protector may protect the motor from the well fluid, and provide pressure equalization between the motor and the wellbore. Indeed, the protector between the motor 104 and pump intake 106 generally isolates the motor from the well fluid. Other protective devices, such as a check valve, drain valve, etc. may be located above the pump 102 discharge. In examples, the check valve may close on shut down of the unit. The ESP system 100 components may include the pump 102, motor 104, seal-chamber section, and surface components 110 such as surface controls. As indicated above, an ESP 100 typically has the surface equipment 110 such as an electrical transformer and system controller. Some ESP 100 examples include a variable frequency drive. Also, ESP 100 components may include a power cable and motor lead extension. For instance, an electrical main cable and a cable motor-lead extension may connect surface equipment with the ESP motor 104 and a well-monitoring device.

Lastly, some ESP 100 examples may include a gas handler or gas separator with integral intake at or near (or combined with) the pump base, or a gas handler with intake at or near the pump base. Gas separators may be employed where free gas causes interference with pump performance. The gas separator may separate some free gas from the fluid stream entering the pump to improve pump performance. Yet, in certain examples of the pump 102 as a helico-axial pump with no radial or mixed-flow pump, a gas separator is not employed. Indeed, some ESP 100 embodiments with the helico-axial pump and PMM do not have this gas separator because the need for such a gas separator may be precluded. In other words, significant benefit may not be realized with the gas separator. For radial or mixed-flow ESPs, the gas handler if employed may be short in length, such as about 7 feet or less, with a small number of stages and configured for a specific flow rate range.

The radial or mixed-flow ESP which may include the pump, protector, motor, intake such as a bolt-on intake, and gas handler, generally operates at nominal speed of 3500 rpm (60 Hertz or Hz) at the high end and with a typical variation between 2000 rpm to 4000 rpm. In contrast, while examples of the present helico-axial pumps may have a similar length of the radial or mixed-flow ESP, the nominal rotation speed for certain embodiments of the helico-axial ESP may be in a range from 3500 rpm, 4000 rpm, or 4500 rpm to 7000 rpm, 7500 rpm, or 8000 rpm. This ESP 100 system with the helico-axial pump and higher rotation speeds may accommodate critical speeds and bearings clearances for the subject speed, and the impeller sized for the flow-rate range.

FIG. 2 is an oil and/or gas production site 200 including a hole or wellbore 202 drilled into the Earth 204 (formation). A wellbore casing 206 is positioned in the wellbore 202. The casing 206 may have holes, slots, or perforations 208 or open hole to receive hydrocarbon fluid 210, such as oil and gas, from the formation. The perforations 208 may extend through the casing 206 wall and any annulus cement 211 into the formation 104. In the illustrated embodiment, the ESP pump 102 with coupled motor 104 are lowered into the wellbore casing 206. In operation, the ESP pump 102 receives the hydrocarbon fluid 210, applies pump head to the fluid 210, and discharges the fluid 210 through a production conduit 212 toward the Earth surface 214, as indicated by arrow 216. As mentioned for high gas volume fraction, a gas separator may not be needed with the ESP pump 102 as a helico-axial pump. After all, the multi-stage helico-axial pump at relatively high speed can handle (process, pump) fluids having high free-gas content. Indeed, the helico-axial pump itself may act as a compressor with respect to certain aspects.

As discussed above with respect to FIG. 1, the ESP 100 may have surface components 110 disposed at the Earth surface 214. The surface components 110 may include fixed-speed or variable-speed controllers and drives. In certain embodiments, a smart or intelligent remote terminal unit (RTU) programmable controller (for fixed-speed or variable-speed) maintains flow of electricity to the pump 102 motor 104. The control package may facilitate the well to operate continuously or intermittently, or be shut off, provide protection from power surges or other electricity changes, and the like. As also discussed, the surface components 110 may include a power cable. In some embodiments, the cable is connected to a top portion of the motor 104, runs up the side of the pump 102, is strapped to the outside of the production tubing from the motor to the surface of the well, and is extended on the surface to, for example, a control junction box. Power cables may have a metal shield to protect the cable from external damage. Lastly, the ESP system 100 may include a downhole sensor and companion surface interface unit to provide for retrieval of real-time system and wellbore performance parameters. Multi-data channel sensors can measure intake pressures, wellbore and motor 104 oil or winding temperature, pump 102 discharge pressure, vibration, current leakage, and flow rate. The ESP system 100 control and alarms may be implemented via real-time monitoring of downhole readings.

FIG. 3 is an ESP 300 having a pump 302 that may be a radial pump, a screw-stator pump, or a mixed-flow or mixed-stage pump, and the like. Indeed, the pump 302 stages can be classified as either radial, mixed, or hybrid flow. The pump 302 may be a screw-stator pump. If so, the inner surface of the pump 302 stator may have grooves to engage the screw shaft or rotor. Moreover, in the illustrated example, the ESP 300 has a motor 304 that is an induction motor which provides pump rotation in a range, for example, of 2000 rpm to 4000 rpm. In the illustrated embodiment, the ESP 300 or pump 302 includes an intake 306 which may be a fluid inlet or suction for the pump 302. In examples, the intake 306 may have one or more openings 307, such as holes, ports, or orifices, to receive the fluid to be pumped. In certain embodiments, the intake 306 is screened. For instance, the intake 306 may have a mesh or screen as its outer surface or outer diameter. A seal section or protector 308 is disposed between the motor 304 and the intake 306. The protector 308 may have a seal type as a labyrinth-type protector or bag-type protector, or other type of protector.

The ESP 300 may include a gas handling system which may reduce the free gas entering the pump 302. The gas handling system may include or be associated with a gas avoider, a gas separator such as a rotary and vortex gas separator, or gas handler such as a helico-axial gas handler. A gas separator of the handling system may prevent or reduce cycling, gas lock, and cavitation of the pump 302. In some examples, the gas handling system may be a multiphase helico-axial pump disposed between the intake 306 and the pump 302.

In the illustrated embodiment, a gas handler 310 device is below the radial or mixed-flow pump 302 and is operated at rotation speeds between 2000 rpm to 4000 rpm. The gas handler 310 device may reduce the volume of free gas and make the incoming multiphase fluid more homogeneous before the multiphase fluid flow reaches the radial or mixed-flow pump 302. However, the ESP 300 system at most can handle free gas up to 75% by volume and also can be limited in applications where gas slugging occurs. A limitation of a gas handler 310 device may be that the handler 310 does not increase the fluid pressure significantly in operation due to the relatively low operating speed and the limited quantity of stages. In addition, the closed pump 302 stages (radial or mixed) limit capability to handle gas and make the pump 302 susceptible to becoming locked by the gas. The ESP 300 may not be applicable for gas wells where deliquification or dewatering is implemented to forward gas to the surface.

Lastly, in the illustrated example of FIG. 3, ESP 300 components are depicted as disposed down in a casing 312 of a wellbore 314 in a hole of an Earth formation 316. The ESP 300 may be connected to a production tubing 318 via a coupler 320. The ESP 300 may receive production fluid from the Earth formation 316 through perforations 322 in the casing 312 or open hole and discharge the production fluid through the production tubing 318 toward the Earth surface. The ESP 300 will also generally have or be engaged with surface components 110, such as those previously discussed.

FIG. 4 is an ESP 400 having a pump 402 that may be a multi-stage helico-axial centrifugal ESP, and the like. As discussed below, the ESP 400 may have a pump 402 intake, motor protector, power cable, motor lead extension, sensor, and so forth. A multiphase helico-axial pump 402 may be a multi-stage rotodynamic pump. Each pump stage (see, for example, FIG. 4A) may have an impeller or vanes and a static diffuser. Thus, the pump 402 may have open hydraulic channels which accommodate solid particles in the flow. A multistage helico-axial pump may be characterized as a centrifugal displacement pump having rotating vane impellers and stationary diffusers. In certain examples, the helico-axial pump 402 may act as a compressor having a rotor and a plurality of compression stages, so that the multiphase mixture can be compressed step-wise to a higher density. In some embodiments, the ESP 400 does not include an additional pump to receive the production fluid from the helico-axial pump 402. The ESP 400 does not include a radial pump, a mixed-flow pump, a screw pump, or a screw-stator pump.

In this example, the ESP 400 has a motor 404 that is permanent magnet motor (PMM) which provides rotation, for example, in a range of 4000 rpm or 4200 rpm or 4500 rpm to at least 7000 rpm. In some examples, the rotation is at least 7500 rpm or at least 8000 rpm. A permanent magnet motor may be a brushless electric motor employing permanent magnets. In examples, the PMM may be more efficient than an induction motor or a motor with field windings.

As discussed, multistage helico-axial pumps 402 may pump mixtures of oil, natural gas, water, sand, and so forth, with gas volume fractions from zero to 97% or even above. The helico-axial stage has a high specific-speed (Ns) design which relies on relatively high rotation speed. The speed may be higher for applications where the impeller diameter is small due to space limitation as is the case with certain oil and gas wells. The multi-phase pump stage at higher rotation speed may accommodate higher gas volume fractions.

Again, some ESP 400 examples do not additionally employ a radial or mixed-flow pump. Moreover, the ESP 400 does not include a screw-stator pump nor grooves on an inside surface of the ESP 400 pump casing. Indeed, multi-phase pumps 402 can be more efficient at higher rotation speed and such is generally less limited than with radial or mixed-flow stage pumps, or screw or screw-stator pumps.

Furthermore, engineering techniques provide for applicable helico-axial pumps 402 that provide higher lift without the radial or mixed-flow pumps to deliver desired flow rates. In this way, the capability to handle gas volume fractions of up to 97% or greater can be achieved in some examples. Thus, certain embodiments of the present techniques may produce wells with gas volume fractions from zero to 97% or more. In contrast, instances of electrical submersible pumps as a radial or mixed-flow pump can only effectively operate with gas volume fractions less than 75%, 70%, 65%, or lower.

The ESP 400 may include an intake 406 and a protector 408 both similar to such components discussed with respect to the preceding figures. In examples, the intake 406 may have one or more openings 407, such as holes, ports, or orifices, to receive the fluid to be pumped. In embodiments, the ESP 400 does not include a gas handling system or gas handler. After all, the helico-axial pump 402 may generally readily pump fluid with a high gas-volume fraction.

In the illustrated example of FIG. 4, ESP 400 components are depicted as disposed down in a casing 312 of a wellbore 314 in a hole of an Earth formation 316. The ESP 400 may be connected to a production tubing 318 via a coupler 410. The ESP 400 may receive production fluid from the Earth formation through perforations 322 in the casing 312 or open hole and discharge the production fluid through the production tubing 318 to the Earth surface. The ESP 400 may have surface components 412, similar or the same as the surface components 110 discussed with respect to the preceding figures. ESP surface components 412 may include a transformer, motor controller, variable speed drive, junction box, cable venting box, wellhead, etc.

FIG. 4A is an exemplary helico-axial stage 420 of the pump 400 of FIG. 4. The illustrated embodiment depicts the portion of the shaft 422 of the pump 400 for the pump stage 420. In operation, the fluid being pumped enters the impeller section 428 of that pump stage 420, as indicated by reference numeral 426. The rotating impeller 428 and stationary diffuser 430 impart pump head to the fluid and discharge the fluid with increased pump head from the stage 420 to the next pump stage and so on, as indicated by reference numeral 432. The diffuser 430 vanes may be open as depicted or instead closed as indicated by dashed lines 434. The pump 400 may have an outer portion 424 which may part of the diffuser 430, or a shroud, casing, enclosure, housing, etc.

Referring to FIGS. 4 and 4A, in general for an ESP 400, the subsurface components include a pump 402 portion and a motor 404 portion, with the motor 404 downhole from the pump 402. The motor 404 rotates a shaft 422 that, in turn, rotates pump impellers 428 to lift fluid through production tubing 318 to the surface. The pump 402 can be multi-stage unit with the number of stages 420 determined by operating requirements. Each stage 420 may include an impeller 428 and diffuser 430. Each impeller 428 is coupled to the rotating shaft 422 and accelerates fluid from near the shaft 422 providing an axial flow that may be relatively smooth. The fluid then enters the non-rotating diffuser 430, which is typically not coupled to the shaft 422 and may contain vanes that direct fluid toward the next pump stage. This diffuser 430 may be stacked with the other diffusers 430 (not shown), and compressed with each other within the pump housing. As discussed, the ESP 400 assemblies may also include seals coupled to the shaft 422 between the motor 404 and pump intake 402, screens to reject sand, optionally fluid separators at the pump, and miscellaneous ESP completions mentioned earlier.

The pump 400 can generally handle free gas in oil wells. In particular, these embodiments of the pump 400 can pump or compress fluid have a gas volume fraction up to 75%, 80%, 85%, 90%, 95%, 97% or even higher. Size ranges of the pump 400 may be a product line of centrifugal pumps with the helico-axial stage type. These pumps may operator at rotation speeds in a range of 4000 rpm (or 4200 rpm, 4500 rpm) to at least 7000 rpm (or 7200 rpm, 7500 rpm, 8000 rpm), and so forth, as the output rotation speed of the electrical submersible PMM 404. Modification or sizing of the pump 402 intake 406 and protector 408 may be implemented for even higher rotation speeds. In contrast, ESPs with a radial pump, mixed-flow pump, or screw-stator pump employ typical intakes and typical protectors.

With embodiments herein, the localized heating including on the rotating sub-components of the ESP system, such as the pump, intake, protector, and motor, might be higher than the typical ESP system. This is because of the higher rotation speed and the lower lubrication or cooling due to the lower content of liquid. This is why, some sub-components materials of each ESP component might be constructed of upgraded material. The higher speed and the lack of liquid may generate heat build-up at the radial bearings. Consequently, the material of the bearings might be specified with clearance to compensate for material expansion due to the additional heat build-up. The protector 408 may also have a thrust chamber which to withstand a certain axial load from the pump 402. With the higher speed, a higher axial load may be generated and thus thrust chamber on the protector 408 configured and sized accordingly. Traditionally, the material for the bearings are bronze, tungsten carbide (TC), and ceramic. The TC and ceramic may function adequately at the higher rpm and low liquid content. On the other hand, other materials for the bearings with low coefficient of thermal expansion may be utilized.

For high gas-oil ratio (GOR) wells that cannot produce naturally to meet the target rates, conventional ESPs techniques generally cannot be implemented due to the limited gas-handling capability of conventional ESPs. Thus, with conventional systems, gas wells that produce a relatively low-amount of liquid and cannot produce naturally, can be problematic. Moreover, oil and gas wells that produce high content of solids can be problematic. In contrast, with present embodiments, a multi-stage helico-axial pump runs up to 7000 rpm or greater for high GVFs above 75% and develops the lift for different flow rates.

Electricity is typically provided to the site by a commercial power distribution system. ESP surface components 412 may include an electrical supply system. In some examples, a transformer may convert the electricity provided via commercial power lines to match the voltage and amperage of the ESP motor 404. As discussed, motor controllers may be a fixed-speed controller or variable-speed controller, or other type of controller. The ESP 400 system can include a variable frequency controller so that the ESP 400 operates over a broader range of capacity, head, and efficiency. The speed of an ESP motor 404 may be proportional to frequency of the electrical power supply. Thus, by adjusting the frequency, the speed can be adjusted, which may be a purpose of the variable speed system. Such may contribute to extending the range of a submersible pump and boosting production. Also, if the production capacity of a well is not precisely known, a variable speed controller can be selected for an estimated range of and adjusted for the desired production level once more data is available. Motor controllers may be digital controls having a system unit that performs shutdown and restart operations, and can be mounted, for example, in the low-voltage compartment of the control panel. In some examples, motor controllers may also include a display unit. This unit may display readings, set points, alarms, and so forth.

Embodiments provide for manufacturing execution of ESP 400 examples including the pump 402 for series size and flow-rate capacities. The implementations may provide for design, assembly, and testing to give flow capacities, configuration and fabrication of the intake and protector, and so on. In one example, a horizontal test bench is implemented for variations of the pump 402. The actions to specify a pump 402 stage flow capacity for a pump 402 series and to specify the intake 406 and protector 408 configurations are applied. Established may be design input, assembly, testing activities, and time and cost to complete the project. Design and procurement can be further considered. For the selected pump series size and established flow rate capacity, a shape of the impeller and diffuser may be configured such as via computational fluid dynamics and executed code applicable to design and optimization of a helico-axial multi-phase pump stage. Pump 402 performance curves for pumped fluids having differing gas volume fractions (GVFs) and at a specified pump 402 rotational speed such as 7000 rpm are determined with the pump parameters such as operating flow rate range, axial thrust load, shut-in pressure, power consumption, efficiency, etc. Considered may be the size and fabrication of other pump 402 sub-components such as the shaft, housing, head, base, bearings, etc. The material specification may be evaluated and applied for the relatively higher rpm and higher GVFs. Once the pump stage is specified, drawings, casting/machining requirements, and material specifications can be established to proceed with the pump stage procurement. Pump assembly drawings and bill of material (BOM) can be reviewed and updated, as needed. Assembly procedures may be prepared or reviewed before or after procurement.

Development and testing may be enacted. After the pump 402 components are procured, assembly can be performed for different pump 402 housing lengths. As examples of the pump 402 are for multi-phase flow, the horizontal testing bench facility may be constituted accordingly to test the pump 402 at different GVFs and at a rotating speed, for example, of at least 7000 rpm. Acceptance criteria can be established. Several pump assemblies and testing may be performed at different stages of the design and development to meet design input. Pumps 402 with different stage types may be assembled to meet the difference between input flow rate and discharge flow rates including for pumped fluids with high GVF values. When the pump performance parameters are known or specified, the intake 406 and protector 408 can be specified to handle the axial-pump thrust load. At that time, it may be beneficial to establish drawings and manufacturing for components such as the thrust chamber of the seal. After the above ESP components are manufactured, testing the unit with a permanent magnet motor can be performed, for example, in a water well. Again, as the subject system is designed to handle multi-phase flow rates, testing the ESP system at different GVFs in a well capable to accommodate such testing may be advantageous.

FIG. 5 is a method 500 of operating an ESP or ESP system. At block 502, the subsurface components of the ESP are lowered into a wellbore. For instance, the ESP subsurface components, such as the pump and motor, while at the surface may be attached to the downhole end of a tubing string for deployment, and then lowered into the wellbore along with the tubing. As mentioned, ESP systems may consist of both surface components such as those housed in the production facility or oil platform, and subsurface components in the well hole or wellbore.

After being lowered (block 502) into the wellbore and situated for operation, the well fluid to be pumped may be received (block 504), for instance, from the Earth or formation through perforations in the well casing or open hole. The fluid may include hydrocarbon such as oil and gas, as well as contaminants and other compounds. The action of the ESP lifting or pumping the well fluid or production fluid may be composed of the actions of blocks 504, 506, and 508.

At block 504, the fluid to be lifted or pumped is received at an inlet of the ESP pump and into the pump. The inlet may be a fluid intake or fluid suction, and may have a screen in certain examples. The inlet may be on a lower portion or suction portion of the ESP pump, or disposed between the pump and motor, or between the pump and a motor protector, and the like. The fluid may be received through the ESP inlet into inside of the ESP pump.

At block 506, the ESP pump applies pump head to the fluid received into the pump through the inlet. In one example of the ESP pump as a centrifugal pump, the pump head is imparted via a rotating impeller (and a stationary diffuser). The ESP may provide pump head for the total dynamic head (TDH) to lift or pump the desired weight or volumetric capacity of production fluid. The applied head may include head to overcome friction losses in the production tubing and surface piping, and to overcome elevation changes.

At block 508, the ESP discharges the pumped fluid through a production conduit to the surface. Lastly, the dashed line 510 is denoted for some examples in which the method 500 of FIG. 5 represents two general actions or methods. In other words, in those examples, a first action may be to lower 502 the ESP subsurface components into a wellbore. A second general action may be to perform the pumping acts indicated in blocks 504, 506, and 508.

Surface pumping systems are not applicable as an ESP or for downhole implementations in oil wells because the surface pumps cannot fit in or accommodate the outside diameter (OD) of the wellbore. Oil wells are completed typically with casing inner diameter (ID) or nominal diameter of 4.5″, 5½″, 7″, 9⅝″, and the like. In addition, surface-pump features preclude applicability of surface pumps as ESPs in oil wells. Surface pumps do not fit or possess an applicable shape and are also a different concept and configuration than ESPs. Sub-sea systems, such as with a gear train, are similarly inapplicable as an ESP or for downhole in a wellbore. However, the pump 402 can be used horizontally in surface coupled to surface electric motors.

Moreover, in view of costs, maintenance requirements, environmental impact, efficiency and flexibility, both downhole and surface applications may benefit from multistage centrifugal pumping systems. Each pump stage is formed by combining an impeller and a diffuser with the matched rotating impeller keyed to the pump shaft. This creates the lifting force or head. In examples, the diffuser directs fluid to the next impeller and does not rotate. Pump efficiency and head generation may be a function of the diameter of the impeller and the rate of rotation. Typically, the smaller the diameter of the impeller, the less head generated, which results in more stages and longer pumps to pump multi-phase fluids at the surface or raise fluid from a reservoir to the surface.

Lastly, the aforementioned ESP features discussed above with respect to FIGS. 1-5 may be interchanged or combined to form differently arranged ESPs in accordance with embodiments of the present techniques. For example, the ESP 400 may incorporate features of ESP 300, or vice versa.

In summary, embodiments include an ESP system including a pump that is a multi-stage helico-axial centrifugal pump for insertion into a wellbore and to lift fluid from the wellbore. The ESP system includes a motor that is a submersible PMM for insertion into the wellbore and to drive the pump. The pump may be coupled to the motor. In examples, the pump is configured for a rotation speed of at least 4500 rpm or at least 7000 rpm, or in a range of 4000 rpm to 7000 rpm. The fluid may include hydrocarbon, oil and gas, and so on, and in certain examples, has a gas volume fraction up to 75% or 80%, or greater. In examples, the ESP system does not include an induction motor, a radial pump, a mixed-flow pump, a screw pump, or a screw-stator pump. Moreover, for some examples, the ESP does not include a gas separator or separate gas handler but the ESP can still readily pump fluid having a gas volume fraction up to 75%, 80%, 97%, or greater.

Another embodiment is a method of operating an ESP, including pumping, by the ESP, fluid from a wellbore, wherein the ESP includes a multi-stage helico-axial centrifugal pump and a PMM. The pumping may include lifting the fluid from the wellbore and discharging the fluid through a production conduit to an Earth surface. Further, the method may include receiving the fluid at an inlet suction of the ESP from perforations in a casing of the wellbore. The method may include operating the multi-stage helico-axial centrifugal pump at a rotation speed of at least 4500 rpm. The pumped fluid may include hydrocarbon or oil and gas, and have a gas volume fraction of at least 75%. In some examples, the ESP does not include a radial pump, a mixed-flow pump, a screw-stator pump, or an induction motor. The method may include lowering a downhole portion of the ESP into the wellbore.

Yet another embodiment is a method of producing oil and gas, including receiving oil and gas from a wellbore to a multi-stage helico-axial centrifugal pump, driving the helico-axial centrifugal pump with a submersible PMM, and lifting the oil and gas from the wellbore via the multi-stage helico-axial centrifugal pump. The submersible PMM may be coupled to the pump. In some examples, the lifting of the oil and gas does not utilize or involve a radial pump, a mixed-flow pump, a screw-stator pump, or an induction motor.

A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. 

What is claimed is:
 1. An electrical submersible pump (ESP) system comprising: a pump comprising a helico-axial centrifugal pump to lift fluid from a wellbore; and a motor comprising a submersible permanent magnet motor (PMM) to drive the helico-axial centrifugal pump.
 2. The ESP system of claim 1, wherein the helico-axial centrifugal pump comprises a multi-stage helico-axial centrifugal pump configured for a rotation speed of at least 4500 revolutions per minute (rpm).
 3. The ESP system of claim 1, wherein the fluid comprises hydrocarbon, and wherein the helico-axial centrifugal pump comprises a rotation speed in a range of 4000 rpm to 7000 rpm.
 4. The ESP system of claim 1, wherein the fluid comprises oil and gas, and wherein the ESP system is configured to pump the fluid having a gas volume fraction of at least 80%.
 5. The ESP system of claim 1, wherein the ESP system does not comprise an induction motor.
 6. The ESP system of claim 1, wherein the ESP system does not comprise a radial pump, a mixed flow pump, or a screw-stator pump.
 7. The ESP system of claim 1, wherein the ESP system does not comprise grooves on an inside surface of a casing of the pump.
 8. An electrical submersible pump (ESP) comprising: a multi-stage helico-axial centrifugal pump for insertion into a wellbore to pump fluid from the wellbore; and a submersible permanent magnet motor (PMM) for insertion into the wellbore and to drive the multi-stage helico-axial centrifugal pump.
 9. The ESP of claim 8, wherein the ESP does not comprise an induction motor
 10. The ESP of claim 8, wherein the multi-stage helico-axial centrifugal pump is coupled to the submersible PMM and configured for a rotation speed of at least 7000 revolutions per minute (rpm).
 11. The ESP of claim 8, wherein the ESP does not comprise a gas separator, and wherein the ESP is configured to pump fluid having a gas volume fraction of at least 75%.
 12. The ESP of claim 8, wherein the ESP does not comprise a radial pump, wherein the ESP does not comprise a mixed-flow pump, and wherein the ESP does not comprise a screw-stator pump.
 13. A method of operating an electrical submersible pump (ESP), comprising pumping, by the ESP, fluid from a wellbore, wherein the ESP comprises a multi-stage helico-axial centrifugal pump and a permanent magnet motor (PMM).
 14. The method of claim 13, comprising lowering a downhole portion of the ESP into the wellbore.
 15. The method of claim 13, wherein pumping comprises lifting the fluid from the wellbore and discharging the fluid through a production conduit to an Earth surface.
 16. The method of claim 13, comprising receiving the fluid at an inlet suction of the ESP from perforations in a casing or open hole of the wellbore.
 17. The method of claim 13, comprising operating the multi-stage helico-axial centrifugal pump to rotate at least 4500 revolutions per minute (rpm), wherein the fluid comprises hydrocarbon.
 18. The method of claim 13, wherein the fluid comprises a gas volume fraction at least 75%.
 19. The method of claim 13, wherein the fluid comprises oil and gas, and wherein the ESP system does not comprise an induction motor.
 20. The method of claim 13, wherein the ESP does not comprise a radial pump, wherein the ESP does not comprise a mixed-flow pump, and wherein the ESP does not comprise a screw-stator pump. 